Thermoformed trays are used by the packaging industry to hold various perishable food items. One of the largest applications for these types of trays is to hold fresh meat. Historically, expanded polystyrene (EPS) trays have been utilized by local butchers and grocers to contain fresh meat that is prepared by in-store butchers. However, the meat packaging industry is undergoing drastic changes whereby meat is butchered in a remotely located facility and freshly packaged into case-ready containers to be shipped to the grocer, with no need for additional repackaging. This reduces the need for local butchers, but also requires the trays to exhibit sufficient gas barrier properties. Typically, the trays will need to have sufficient barrier properties to ensure the packaged meat has a shelf life of between about 8 to 12 days, enough for packaging, transport, and presentation in the store.
Due to its excellent stiffness, clarity, high temperature resistance, barrier properties and cost, polypropylene has been utilized as a replacement for EPS in thermoformed meat trays. While polypropylene solutions can provide acceptable stiffness and toughness when the appropriate impact modifier is utilized, they typically cannot provide the balance of stiffness, toughness and optics required for many applications.
What is desired is a composition that can be readily formed into thermoformed trays that exhibit an excellent balance of stiffness, toughness and optics. Additionally, it is desirable for the trays to resist stress whitening when manipulated and handled.
Objects of the Invention:
One object of the invention is to provide a composition which can be made into sheets that can be readily formed into thermoformed articles, preferably trays and containers exhibiting an excellent balance of stiffness, toughness and optical properties, such as high clarity and/or low haze.
Another object of the invention is for the thermoformed articles, such as trays, to exhibit the above-mentioned properties and, further, exhibit good resistance to stress whitening.
Still another object of the invention is that the thermoformed articles, preferably trays and containers, exhibit sufficient vapor barrier properties to enable fresh food items contained by the trays and containers to have a suitable shelf life.
A further object of the invention is to provide a composition containing an impact modifier that is very miscible with polypropylene and therefore can be easily blended, even under poor mixing conditions.